Compressibility
Loftier bags (and warmer ones) tend to take more effort to compress and the Neutrino Endurance 600 is about average in that respect. It does not compress as small as many of the other bags in the category; it is among the largest of bags compared to others in this category.

Warmth
The RAB Neutrino Endurance 600 has 800+ down fill and uses a Pertex Quantum lining that allows the down fill to loft at its maximum – and the loft is enough to create a very warm and cozy bag comparable to other bags in this category that have greater loft. It also uses hydrophobic down, treated for faster drying, absorbing less water and greater loft retention (ultimately improving the down performance). Additional features, like an extremely generous draft tube and close fitting neck baffle design help eliminate drafts and cold spots, as does its shorter size. Users found this bag warm in temperatures dipping into the mid 20s. 

Features
In RAB bags, those women-specific features translate into shorter length (one size only to a maximum user height of 5’7”), narrower shoulder area and wider hip area. RAB manages this extremely effectively—providing the user does not have an issue with the height restriction.

The Pertex Endurance outer fabric (also included internally in the hood and neck areas) is extremely durable (being the same fabric that RAB uses on its down jackets) making it even better suited to damp conditions than some other lining fabrics. This is also why RAB advertises this product as particularly useful for alpine bivy ledges, lightweight backpacking in inclement weather (or for year round use in tents).

The Neutrino Endurance 600 uses a mummy taper shape with an angled foot box, strategically giving space where needed while preserving warmth factor. The zipper uses anti-snag zipper webbing tape which users found effective (and reported no issues with snagging). The Neutrino Endurance 600 is hand filled in Derbyshire UK. The inside zippered pocket is suitable for small items you may wish to keep close to you, such as a music source, tissues or similar items.   

There is a weird design issue on the top left of the bag where the neck baffle intersects with the draft tube which also happens to be where the zippered pocket lays. It isn’t terribly problematic since it adds a bit more insulation in the neck area and you really can’t feel it when sleeping, even if it is a little cumbersome. 

Overall Comfort
The women-specific shape, containing the same amount of down as the male version, made for a very roomy and comfortable bag that offers excellent warmth.  I found the hood cinching cord made the hood slightly uncomfortable – when cinched comfortably for the neck area, it was a little tight for the head. Overall, users still found this to be an extremely comfortable and cozy bag (and hood).  

Durability
The Neutrino Endurance 600 held up to wear and tear and showed no marks of use in the testing phase. Its outer shell seems even more robust than many other shells in this category and I would not foresee durability issues with continued use.